Cell clones nonproductively transformed by the replication defective Abelson strain of murine leukemia virus were analyzed for type C viral antigen expression by competition immunoassay. Abelson murine leukemia virus transformed mink nonproducer lines were found to express an 85,000-100,000 molecular weight polyprotein that contained murine leukemia virus gag proteins p15 and p12 covalently linked to a 60,000 molecular weight protein. The latter protein did not express antigenic cross reactivity with other virion-coded gag gene proteins such as p30 and p10, or with other pol or env gene products. By analogy to earlier data on feline and avian sarcoma viruses, these results suggest that the 60,000 molecular weight protein might represent the Abelson murine leukemia virus src gene product and that in translation it is initially linked in precursor form to gag structural proteins.